PHYSICAL GEOLOGY. 



17 



in more than one place. It may be observed that, throughout 

 the gorge above Hsipaw, the course of the river is parallel to a 

 great overthrust fault, which strikes almost due north and south 

 through the rocks at a short distance to the west, and that the 

 plane of this fault is inclined eastwards towards the river. Also 

 that the spurs from the hills on the western bank slope down 

 gradually towards the gorge, whereas on the eastern bank the rocks 

 form a true scarp, rising almost vertically from the water's edge 

 to a height of some 1,500 feet. Moreover, it is significant that 

 remnants of old river terraces, consisting of well-worn boulders and 

 pebbles, are found on the western slopes to a height of 200 or 300 

 feet above the present river level, while on the eastern side no 

 recent boulder or pebble beds have been noticed. It seems prob- 

 able, therefore, that when the river originally took this direction, and 

 was flowing at a much higher level than at present, it took 

 advantage of the great dislocation mentioned above, and began by 

 excavating its course along it, and that, fo. lowing the general dip 

 of the "strata, which is easterly, it has gradually cut back to its 

 present position. It seems not unlikely, too, that when the river 

 first began to flow in this direction, the limestone, which now 

 crowns the scarp on the eastern bank, extended considerably 

 further westwards, and that the valley originated as a limestone 



gorge- 

 Besides the great overthrust fault mentioned above, there are 

 ^ f f ^ several other faults of a normal kind which 



have assisted in determining the course taken 

 by the river. Some of these faults must be of rather recent de- 

 velopment, speaking in a geological sense, for they still form con* 

 spicuous surface features. Such are the fault scarps along the north- 

 ern edge of the Hsipaw valley ; a fault running along the Nam-Tu 

 valley for several miles above Tong-ang ferry ; and the great fault 

 scarp running south from Kyaukkyan (D 3), which forms such 

 a conspicuous feature in (lie landscape as we descend from Maymyo 

 towards Hsum-Hsai. At the point where the Nam-Tu crosses this 

 fault the river is suddenly deflected northwards, forming a narrow 

 loop of several miles m length. 



The frequent sudden changes in the course of the Nam-Tu, and 



the fact that in almost every case where such 



Relation to trilmtaiies. , . . . . . 



a change in direction occurs, a considerable 

 tributary joins the main stream, and the combined waters follow 



o 



